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Grand Teton National Park Geologic Resource Evaluation Scoping Report

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Grand Teton National Park Geologic Resource Evaluation Scoping Report Grand Teton National Park Geologic Resource Evaluation Scoping Report Sid Covington and Melanie V. Ransmeier Geologic Resources Division Denver, Colorado August 22, 2005 Table of Contents Executive Summary........................................................................................................ ii Introduction..................................................................................................................... 1 Geologic Setting.............................................................................................................. 2 Geologic History............................................................................................................. 4 Significant Geologic Resource Management Issues....................................................... 7 Earthquake Hazard Assessment and Planning............................................................ 7 Fluvial Geomorphology.............................................................................................. 8 Glacial and Peri-glacial Monitoring............................................................................ 9 Cave and Karst Resources ........................................................................................ 10 Hydrothermal Features.............................................................................................. 10 Wetlands ................................................................................................................... 11 Oil and Gas Development......................................................................................... 11 Sand and Gravel Activities ....................................................................................... 11 Historic Mining......................................................................................................... 12 Mass Wasting............................................................................................................ 12 Climbing ................................................................................................................... 12 Paleontology ............................................................................................................. 13 Bentonitic Soils......................................................................................................... 13 Geologic Mapping Status.............................................................................................. 14 Scoping Meeting Participants ....................................................................................... 16 References..................................................................................................................... 17 Area Map ...................................................................................................................... 18 Geologic Map Graphic.................................................................................................. 19 i Executive Summary A Geologic Resource Evaluation scoping meeting for Grand Teton National Park took place on June 21, 2005, at park headquarters in Moose, Wyoming. The following day a geologic field trip highlighted glacial features of the park and of the Jackson Hole area. Scoping meeting participants identified the following geologic resource management issues as having highest priority. 1. Geologic hazard assessment and response particularly as related to earthquakes 2. Stream flow, stream channel morphology and dynamics 3. Glacial and climate change monitoring 4. Disturbed lands restoration These and other geologic resource management topics are discussed in detail on pages 7 to 13. ii Introduction This report briefly describes the general geology of Grand Teton National Park (GRTE), including a geologic history of the park, geologic resource management issues in the park, and the status of Geologic Resource Evaluation (GRE) digital geologic mapping projects related to the park. Meeting participants identified the geologic management issues at a geologic scoping meeting held by the National Park Service Geologic Resources Division (GRD), GRE at park headquarters in Moose, Wyoming on Tuesday, June 21, 2005. The meeting was followed, on Wednesday, June 22, by a geologic field trip highlighting glacial features of the Jackson Hole area The purpose of the GRE scoping meeting was to discuss the status of geologic mapping in the park, the geologic bibliography, and geologic issues affecting Grand Teton National Park. Products derived from the scoping meeting are: (1) a digital geologic map of the park; (2) a geologic bibliography related to the park; (3) a scoping summary (this report), and (4) a GRE report which focuses in depth on the geologic resource management issues affecting the park and relates features and processes to geologic map units present in the park. Grand Teton National Park was established by an act of Congress on February 26, 1929. At this time the park was 96,000 acres in size encompassing only the Teton Range and six glacial lakes at the base of the mountains. The need to protect a larger area as an ecosystem and to prevent unfettered development was recognized but delayed for many years by anti-park sentiment in the local community. Franklin D. Roosevelt established the 221,000- acre Jackson Hole National Monument by presidential proclamation in 1943. The monument was composed of Teton National Forest acreage, other federal properties including Jackson Lake, and a generous 35,000-acre donation by John D. Rockefeller, Jr. It was not until September 14, 1950, that the original 1929 park and the National Monument were united as Grand Teton National Park, creating the present-day boundaries encompassing about 310,000 acres (Skaggs 2000). 1 Geologic Setting Grand Teton National Park is located in the Middle Rocky Mountain physiographic province that divides the Wyoming basin to the southeast and the Columbia River Plateau to the west (Figure 1). Much of the Middle Rocky Mountain province, including GRTE, is located within the intermountain seismic belt (ISB) an arc-shaped zone of earthquake activity that trends north-south through the intermountain west from northwestern Montana in the north, through Wyoming, Idaho, and Utah, and southern Nevada/northern Arizona to the south. The ISB separates the Rocky Mountains and the Colorado Plateau on the east from the Basin and Range province to the west. Tensional tectonic forces within the expanding Basin and Range province are responsible for creating the Teton, Wasatch, Hebgen Lake, and other major faults within the ISB (Smith and Siegel 2000). The Teton fault is an active normal fault that traces the eastern front of the Teton Range and is largely responsible for creating the modern Teton landscape. Most earthquakes in the ISB are shallow, occurring at depths less than 20 kilometers (12 miles). Fifty moderate-to-large (magnitude 5.5 to 7.5) earthquakes have occurred in this zone since 1900; the two largest were the 1959 Hebgen Lake, Montana earthquake (magnitude 7.5) and the 1983 Borah Peak, Idaho earthquake (magnitude 7.3) (http://www.seis.utah.edu/edservices/EES/ISB.shtml). GRTE is essentially composed of two landforms; the Teton Range and Jackson Hole. On the western side of the Teton fault is the Teton Range a narrow, west-tilting, upthrown mountain block (horst) nearly 73 kilometers (45 miles) in length. Jackson Hole is the corresponding downdropped fault block (graben) east of the Teton fault. The Teton fault which separates these features has experienced several thousand magnitude 7 – 7.5 earthquakes over the past 13 million years. Today the highest peaks in the Teton Range rise nearly 2,134 meters (7,000 feet) above the valley floor. Scientists estimate that the floor of Jackson Hole has down dropped around 7,877 meters (16,000 feet) over the past 13 million years. The total amount of vertical offset along the Teton fault is difficult to calculate because rock eroded from the Teton Range and has been transported and deposited into the valley by streams and glaciers. Thus, the Tetons have been lowered and Jackson Hole has been filled with hundreds of meters of sediment obscuring the true offset. Using the best available data, scientists estimate that this total offset is near 7,010 meters (23,000 feet) (Smith and Siegel 2000). Seven of the spectacular peaks in this mountain range exceed 3.659 meters (12,000 feet) in elevation. Together these peaks form the Cathedral Group of which, Grand Teton is the highest peak, reaching an elevation of 4,197 meters (13,770 feet). The Teton Range and Jackson Hole have both been dramatically sculpted by Pleistocene glaciation, specifically the Bull Lake and Pinedale glacial advances. During these glacial periods multiple glaciers flowed south from the Yellowstone Ice Sheet and converged in Jackson Hole. Ice up to 610 meters (2,000 feet) thick covered the valley floor. Alpine glaciers originating in the Tetons also formed during this time sculpting the peaks of the range. Glacial features in the GRTE area include: alpine glaciers, snow fields, cirques, U- shaped valleys, moraines, large glacial outwash planes, and glacial lakes. 2 Figure 1: Physiographic location of Grand Teton National Park 3 Geologic History and Stratigraphy Precambrian The oldest rocks in the park are of Precambrian age, from about 2,680 Ma to about 765 Ma old. These rocks are part of the Wyoming craton, one of several tectonic plates that came together to form the Precambrian core of North America (Love et al.
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